Three types of monoamines, known as serotonin, norepinephrine and dopamine, act as neurotransmitters in organisms. Therefore, pharmaceuticals having a monoamine reuptake inhibitory effect are widely used as therapeutic pharmaceuticals for diseases of the central and peripheral nervous systems.
Many of the pharmaceuticals used to date for treating depression selectively inhibit norepinephrine or serotonin reuptake. Examples of such pharmaceuticals include imipramine (a first-generation antidepressant), maprotiline (a second-generation antidepressant), selective serotonin-uptake inhibitors such as fluoxetine (SSRI, third-generation antidepressants), serotonin and/or norepinephrine reuptake inhibitors such as venlafaxine (SNRI, fourth-generation-antidepressants), and the like (see Sadanori Miura, Rinshoseishinyakuri (Japanese Journal of Clinical Psychopharmacology), 2000, 3: 311-318).
However, it takes at least three weeks for these pharmaceuticals to exhibit their therapeutic effects and furthermore, these pharmaceuticals fail to exhibit sufficient effects in about 30% of patients suffering from depression (see Phil Skolnick, European Journal of Pharmacology, 2001, 375: 31-40).